Study of photoluminescence and electroluminescence mechanisms in quantum-confined InSb/InAs heterostructures

Photoluminescence and electroluminescence in InSb/InAs heterostructures with ultrathin InSb insertions grown by molecular-beam epitaxy have been systematically studied. Measurements were made in the temperature range from 2 to 300 K on a large set of samples of various designs, with both the InAs matrix and ultrathin InSb insertions grown by different methods. The primary goal of the study was to identify the main radiative recombination channels in these heterostructures. It is shown that optical transitions associated with acceptor impurity centers in the InAs matrix represent an important mechanism diminishing the efficiency of luminescence from InSb insertions at room temperature. The results obtained are important for development of optimal growth modes and design of the active region of light-emitting devices based on quantum-confined InSb/InAs structures emitting in the range 3–5 μm.     

Improvement of the mechanical characteristics and corrosion resistance of welded joints of maraging steels

We show that the specific character of a structural state of welded joints of Kh11N10M2T steel as a sequence of structural changes in the course of accelerated heating of maraging steels causes a regular inhomogeneity of their mechanical characteristics and low corrosion resistance. We develop a procedure of thermal treatment which guarantees homogeneity of welded joints in strength, plasticity, and toughness. The mechanical characteristics and corrosion resistance of these joints correspond to those of the base metal that is reached due to both removal of interdendritic liquating inhomogeneity of the weld metal and equalization of the structure and phase composition in all zones of a welded joint. Institute of Mechanics, Ukrainian Academy of Sciences, Kiev. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 35, No. 1, pp. 47–54, January–February, 1999.     

Large-magnitude spin polarization of electrons in an InAs-based diode structure

In studying circular-polarized photoluminescence, a high degree of spin orientation of electrons is observed in the n-type region of an InAs-based diode structure in a magnetic field in the Faraday geometric lay-out of the experiment. The degree of polarization is as high as 90% in the field of 2 T. In contrast, the degree of polarization in conventional InAs layers without a p-n junction is not higher than 20% in fields as high as 4 T. This effect is attributed to the built-in field of the p-n junction: the built-in field prevents localization of non-equilibrium electrons at shallow donor centers and, thus, allows orientation of electron spins due to Zeeman splitting in the conduction band.     

Investigation of structural conditions for improving the characteristics of strength, plasticity, and fracture toughness of maraging steels

The structural parameters governing the embrittlement and plasticizing of stainless (Kh12N10MT, Kh11N10M2T, and Kh13N9D2MT) and high-strength (N18M3T and N18K9M5T) maraging steels are analyzed; they are varied by thermal-kinetic conditions, the sequence and multiplicity of various heat-treatment processes such as austenitization, age hardening, and α↔γ-phase transformation in the subcritical temperature range. We justified both the individual and joint influence of austenite grain size and volume fraction of particles of intermediate phases on the regularities of variation and correlation of characteristics of strength, plasticity, and fracture toughness during thermal hardening. We revealed the role of the austenite which is formed during the α→γ-phase transformation in the increased deformability and fracture toughness of the steels under study, taking into account the character of their alloying. Based on the revealed shift in the temperature range of the α→γ-phase re-transformation toward the temperature range of age hardening, we determined the structural conditions for implementing its plastizicing effect on the high-strength state of the maraging steel. Timoshenko Institute of Mechanics, National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 2, pp. 51–61, March–April, 2000.     

Highly sensitive submillimeter InSb photodetectors

Submillimeter photoconductivity of the electron gas in bulk InSb has been studied. A new design of the InSb photodetector in the form of planar coils with a length-to-width ratio of two orders of magnitude is suggested. This design enables fabrication of highly sensitive photodetectors with the responsivity peak tunable by magnetic field.     

Features of Tunneling Current in Superlattices with Electrical Domains

Journal of Communications Technology and Electronics - Abstract—The tunneling electron transport in GaAs/AlAs and InAs/AlSb superlattices with electric domains at room temperature is studied....     

Metal-Semiconductor Nanoheterostructures with an AlGaN Quantum Well and In Situ Formed Surface Al Nanoislands

We report on fabrication and studies of composite heterostuctures consisting of an Al_0.55Ga_0.45N/A_l0.8Ga_0.2N quantum well and surface Al nanoislands, grown by plasma-assisted molecularbeam epitaxy on c-sapphire substrates. The influence of a substrate temperature varied between 320 and 700ºC on the size and density of the deposited Al nanoislands is evaluated. The effect of Al nanoislands on decay kinetics of the quantum well middle-ultraviolet photoluminescence has been investigated by time resolved photoluminescence. The samples with the maximum density of Al nanoislands of 10⁸ cm^–2 and lateral dimensions in the range of 100–500 nm demonstrated shortening of the photoluminescence lifetime, induced by interaction of the emitting quantum well and the plasmonic metal particles.

     

Switching between the mode-locking and Q-switching modes in two-section QW lasers upon a change in the absorber properties due to the Stark effect

The passive Q-switching and mode-locking modes are implemented in two-section lasers with three quantum wells. It is demonstrated that raising the reverse bias on the absorbing section changes its spectral and dynamic properties and, accordingly, leads to a change from the Q-switching mode to mode-locking. The pulse-repetition frequency in the mode-locking mode is 75 GHz, with the product of the pulse duration by the spectrum bandwidth being 0.49, which is close to the theoretical limit. It is shown that, in structures with three quantum wells, strong absorption at the lasing wavelength gives rise to a photocurrent across a section of the saturable absorber, which is sufficient for compensation of the applied bias.